Salt weathering is among the most severe phenomena affecting porous limestone, often leading to the loss of precious material from historical sculptures and building façades. Together with exerting a weathering action, salts can also hamper the success of consolidation treatments, by interfering with consolidants’ penetration and/or curing reactions. On site, application of consolidants on non-contaminated stone is rarely feasible, especially in the case of porous limestones; for this reason, testing application of consolidants on salt laden stone is of particular relevance to guarantee their successful application in the field. In this paper, two hydroxyapatite (HAP)-based treatments have been applied to Lecce Stone, a very porous organogenic limestone, highly susceptible to salt weathering. The two treatments differ for DAP concentration, application procedure and presence/absence of ethanol in the formulation. Prior to treating, specimens were subjected to salt crystallization cycles in a sodium sulphate solution, to cause salt contamination and induce weathering. They were then desalinated, purposely leaving a percentage of salts in the stone (SO42- after desalination ~0.15-0.3 wt%). Phase formation and distribution as a result of different contamination levels were investigated, and the efficacy of the treatments in comparison to ethyl silicate was determined, as it is currently the most used consolidant for this lithotype. Finally, the durability of the most promising treatment to further salt crystallization was evaluated, again in comparison with ethyl silicate. Promising results were obtained, as the presence of sodium sulphate did not prevent the HAP- based consolidants from uniformly distributing in the stone, sealing cracks and forming insoluble phosphate phases. Interestingly, the application on non-desalinated stone revealed that the nature and the amount of the phases that form as a result of the treatment are dependent on the amount of salts in the stone. Finally, most promising HAP-based formulation was found to enhance the stone’s durability towards further salt crystallization, also compared to ethyl silicate.
The application of hydroxyapatite-based treatments to salt-bearing porous limestones: A study on sodium sulphate-contaminated Lecce Stone
Graziani G.
;Sassoni E.;Scherer G. W.;Franzoni E.
2017
Abstract
Salt weathering is among the most severe phenomena affecting porous limestone, often leading to the loss of precious material from historical sculptures and building façades. Together with exerting a weathering action, salts can also hamper the success of consolidation treatments, by interfering with consolidants’ penetration and/or curing reactions. On site, application of consolidants on non-contaminated stone is rarely feasible, especially in the case of porous limestones; for this reason, testing application of consolidants on salt laden stone is of particular relevance to guarantee their successful application in the field. In this paper, two hydroxyapatite (HAP)-based treatments have been applied to Lecce Stone, a very porous organogenic limestone, highly susceptible to salt weathering. The two treatments differ for DAP concentration, application procedure and presence/absence of ethanol in the formulation. Prior to treating, specimens were subjected to salt crystallization cycles in a sodium sulphate solution, to cause salt contamination and induce weathering. They were then desalinated, purposely leaving a percentage of salts in the stone (SO42- after desalination ~0.15-0.3 wt%). Phase formation and distribution as a result of different contamination levels were investigated, and the efficacy of the treatments in comparison to ethyl silicate was determined, as it is currently the most used consolidant for this lithotype. Finally, the durability of the most promising treatment to further salt crystallization was evaluated, again in comparison with ethyl silicate. Promising results were obtained, as the presence of sodium sulphate did not prevent the HAP- based consolidants from uniformly distributing in the stone, sealing cracks and forming insoluble phosphate phases. Interestingly, the application on non-desalinated stone revealed that the nature and the amount of the phases that form as a result of the treatment are dependent on the amount of salts in the stone. Finally, most promising HAP-based formulation was found to enhance the stone’s durability towards further salt crystallization, also compared to ethyl silicate.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
